Dispensers with metering valves have been developed for dispensing volumetrically controlled doses of fluid such as aerosol sprays, foams, creams, gels, and the like.
FIG. 1 illustrates such a valve 10 for use with a container (not illustrated) of pressurized fluid to be dispensed. Preferably, the fluid is pressurized by a gaseous propellant. The propellant is dissolved within the fluid to be dispensed, or liquefied and mixed with the fluid to be dispensed, especially when it is desired to dispense a foam.
The metering valve 10 includes a rigid metering chamber 12 with a valve stem 14 extending therethrough. A lower opening 16 of the metering chamber 12 is connected to an inlet tube 18. The inlet tube 18 extends almost to the bottom of the container for conducting fluid to be dispensed from the container into the metering chamber 12.
A valved inlet passageway 20 is located in the vicinity of the opening 16 and a valved outlet passageway 22 is located at the top of the metering chamber 12. The valved inlet passageway 20 and the valved outlet passageway 22 are selectively opened and closed depending on the position of the valve stem 14. A coiled compression spring 24 biases the valve stem 14 upwardly toward the position illustrated in FIG. 1.
In the position illustrated in FIG. 1, the valved inlet passageway 20 is open and pressurized fluid to be dispensed is forced upwardly through the inlet tube 18 and the passageway 20, and fills the metering chamber 12 until the pressure of the fluid in the metering chamber 12 is equal to the pressure of the fluid in the container. When the valve stem 14 is pushed downwardly, the passageway 20 is closed and the outlet passageway 22 is simultaneously opened. This exposes the fluid in the metering chamber 12 to ambient pressure. As a result, the propellant dissolved or mixed within the fluid expands and the fluid is dispensed outwardly through the passageway 22.
When released, the valve stem 14 is returned by the spring 24 to the position illustrated in FIG. 1, closing the outlet passageway 22 and opening the inlet passageway 20, permitting more fluid to fill the metering chamber 12. In this way, a metered dose corresponding (ideally) to the volume of the metering chamber 12 is dispensed each time the valve stem 14 is pushed downwardly.
The metering valve 10 described above in connection with FIG. 1 is disclosed in detail in U.S. Pat. No. 4,034,899, issued July 12, 1977. Other similar valves are also disclosed in this prior patent. The entire disclosure of U.S. Pat. No. 4,034,899 is incorporated herein by reference.
The amount of fluid dispensed by a dispenser with a metering valve such as the valve 10 is a function of the volume of the valve's metering chamber. Ideally, the amount dispensed would consistently correspond to the volume of the metering chamber so that the amount of each and every dispensed dose could be accurately predetermined. However, prior art metering dispensers have been inaccurate and imprecise. Particularly, such dispensers have been subject to random inter-dose variability.
The problem appears to be that when a dose is dispensed from a metering chamber (such as the metering chamber 12), pressure within the metering chamber is reduced to ambient or atmospheric pressure (or at least a pressure less than the pressure within the container). Then, when pressurized fluid from the container is introduced into the metering chamber, a randomly variable amount of flashing or vaporization (or evolution of propellant gas) occurs as the fluid to be dispensed encounters the relatively low pressure within the metering chamber. As a result, the metering chamber can never be filled entirely by liquid. The drop in pressure and the resulting gas and/or vapor within the metering chamber introduces uncertainty and imprecision into the dispensing process since the amount of gas and/or vapor evolved from the fluid tends to be erratic, or at least cannot be accurately predetermined.
Such inconsistency or imprecision has proven to be a particular problem with prior art dispensers having so-called large-dose metering valves. As used herein, the term "large-dose metering valve" means a metering valve whose metering chamber has a volume of not less than about 200 microliters. Random interdose variability is particularly noticeable when the volume of the metering chamber exceeds 500 microliters.
A "flexible" metering valve 40 is illustrated in FIG. 2. Features of the valve 40 which are similar to the valve 10 are identified by the same reference numerals in the drawings.
The metering valve 40 has an enlarged metering chamber indicated generally at 42. The enlarged metering chamber 42 is formed by supplementing the volume of the rigid chamber 12 of the metering valve 10 with an elastomeric wall 44. The rigid chamber 12 communicates with the space 46 defined within the wall 44 through openings 48.
In operation, when the metering valve 40 is in the position illustrated in FIG. 2, fluid flows upwardly through the inlet tube 18, through the open valved inlet passageway 20, and fills the enlarged metering chamber 42 (both the rigid chamber 12 and the space 46). When the valve stem 14 is pushed downwardly, the passageway 20 is closed and the passageway 22 is simultaneously opened. As in the valve 10, fluid within the enlarged metering chamber 42 then expands outwardly in the direction of atmospheric pressure through the passageway 22. Since the wall 44 is flexible, the pressurized fluid outside of the wall 44 collapses the wall 44 to assist in the dispensing of the fluid from the space 46.
When released, the valve stem 14 is moved upwardly by the spring 24, closing the passageway 22 and opening the inlet passageway 20. Fluid is then forced upwardly through the inlet tube 18 to fill the rigid chamber 12. The space 46 is also filled through the openings 48 because of the resilience of the wall 44 (even though the pressure within the space 46 is never greater than the pressure surrounding the wall 44).
It appears that the wall 44 may actually somewhat reduce the problems associated with vaporization or evolution of gas within the metering chamber 42. However, any benefits are offset by practical variances in the wall's 44 resilient return to the position illustrated in FIG. 2. That is, the wall 44 does not always return to exactly the same position.
The metering valve 40 described above in connection with FIG. 2 is disclosed in detail in U.S. Pat. No. 3,104,785, issued Sept. 24, 1963. Other similar valves are also disclosed in this prior patent. The entire disclosure of U.S. Pat. No. 3,104,785 is incorporated herein by reference.